A standard method to calcine limestone fines into lime is via a continuous gas suspension flash calciner process. In such a process, limestone fines are entrained in a heated process gas which passes upward through a vertically situated flash calciner. The flash calciner is sized and the process gas velocity is selected so that the residence time of the limestone particles within the calciner will typically be limited to from about 1 to 3 seconds. During this time full decomposition of limestone to lime must occur. Due to excellent gas/solids contact this decomposition can be achieved for particles ranging up to a nominal diameter of 0.5-1 mm using acceptable operating temperatures up to 1100-1200° C. Such particles will make up the majority of the particle size distribution of the limestone fines subject to flash calcination. However, larger particles (such as up to a top size of about 4 mm) which constitute a minority fraction of the particles in the flash calciner, require the utilization of much higher gas temperatures than 1200° C. to complete their decomposition within the time constraints set forth above. Therefore, in such a prior art process there is significant non-uniform calcinations across a wide particle size range. In order to simultaneously calcine the larger fraction in a flash calcination system it has been necessary to utilize significantly higher temperatures in the system with correspondingly increasing energy costs while contributing to adverse affects such promoting coating formation, reducing lime reactivity and possibly over-burning the finer particles in the particle mix.
A method to promote the uniform calcination of both the finer and coarser fraction of the limestone fines treated in a flash calcination process without the above adverse effects is needed. In order to be commercially viable, such a method should not add significantly to the complexity, capital cost or operating costs of the system nor add significantly to overall energy consumption.